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Environment International 139 (2020) 105717 Contents lists available at ScienceDirect Environment International journal homepage: www.elsevier.com/locate/envint Typical pesticides diffuse loading and degradation pattern differences under the impacts of climate and land-use variations T ⁎ Wei Ouyanga, , Xin Haoa, Mats Tysklindb, Wanxin Yanga, Chunye Lina, Aihua Wanga a State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100875, China b Environmental Chemistry, Department of Chemistry, Umeå University, SE-901 87 Umeå, Sweden ARTICLE INFO ABSTRACT Handling Editor: Olga-Ioanna Kalantzi Riverine sediment can reconstruct the history of organic pollution loads and can provide reliable temporal Keywords: information for pesticide metabolite dynamics in watershed. Sediment core samples were collected from two Sedimentary pattern riverine sections of a cold watershed base in the presence land use change under agricultural development, and Diffuse pollution the vertical concentrations of four pesticides (atrazine, prometryn, isoprothiolane, and oxadiazon) and two Atrazine degradation atrazine metabolites (deisopropyl-atrazine and deethyl-atrazine) were determined by gas chromatography–mass Pesticide spectrometry. The presence of pesticides and metabolites was detected at different depths (11–17 cm) at 1-cm Watershed modeling intervals along the two sediment cores, and the flux was calculated with a constant rate of supply model based on the observed concentrations and 210Pb isotope radioactivity chronology. By comparing the concentrations and fluxes of pesticides between the two sediment sections, significant differences in accumulation under different land-use patterns were found. Redundancy analysis further indicated that temporal watershed farmland variance was the dominant factor for pesticide loading. The lower concentration of atrazine and the higher concentration of the other pesticides in the estuarine sediment was closely related to the decreasing upland in the upstream area and the increase in paddy fields in the downstream area. The analysis of atrazine and the metabolites indicated that atrazine is more likely degraded to deethyl-atrazine and the metabolites have similar migration processes in the sediments, which can easily migrate downward. Moreover, the ratio of metabolites to atrazine showed that atrazine degradation was intensive during the transport process, but the metabolites efficiency was lower in this area due to the cold temperature. The results provide insights for the management of pesticide pollution control in watersheds and the potential effects of low temperature on the degradation of pesticides. 1. Introduction accumulate in surface water and sediment, which can lead to a lasting potential threat to the aquatic environment (Grung et al., 2015; Kaonga The use of pesticides is of great significance in ensuring food se- et al., 2015, Lapworth et al., 2015). Understanding pesticides’ migra- curity, but with agricultural expansion and the excessive use of pesti- tion, degradation and accumulation in surface water and sediment can cides, the impact of pesticide on ecosystem security has become an offer insights into pesticide pollution management. important issue of global concern (Anderson et al., 2002; Tilman et al., Sediment in the watershed outlet represents the final compartment 2002). Although pesticides are trace agricultural diffuse-source pollu- for pesticide accumulation, which persists for a long time in aquatic tants, the high environmental risk and persistent impact associated with sediments; thus, sediment at the outlet is an effective medium that can pesticides and their related metabolite products cannot be ignored be used to assess the contamination level and identify the sources of (Love et al., 2011; Braun et al., 2019). The transport and degradation contamination of watersheds that have mixed land use (Fairbairn et al., fate of pesticides in agricultural watersheds comprise complex pro- 2015; Bhattacharya et al., 2003). Studies have shown that watershed cesses, which involve hydrolysis, photolysis, adsorption, oxidation, trace organic pollutants are enriched in the sediments, and sediment volatilization, photodegradation, and microbial degradation (Ghattas pollution is more stable over time than are dissolved or suspended et al., 2017; Qu et al., 2017). Most of these pesticides are hydrophobic pollutants; thus the accumulation of pesticides in the sediments can be contaminants; thus, they can be transported from farmland into the used to evaluate the anthropogenic and natural impacts that result from aquatic environment by adsorbing onto soil particles, and they the entire watershed (Ghosh et al., 2016; Chapman et al., 2013). In ⁎ Corresponding author. E-mail address: [email protected] (W. Ouyang). https://doi.org/10.1016/j.envint.2020.105717 Received 30 December 2019; Received in revised form 24 March 2020; Accepted 2 April 2020 Available online 10 April 2020 0160-4120/ © 2020 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/BY/4.0/). W. Ouyang, et al. Environment International 139 (2020) 105717 addition, because the sediment is a sink for pollutants, the type and selected, both of which had a small slope of 5 degrees and no river concentration of the pesticides in sediment in different riverine sections branch or sand mining. The first section (S1) was located at the wa- can also reflect the spatial distribution of land use and the differences in tershed outlet, which has paddy land in the downstream area, and the crop tillage management (Moran et al., 2017). second section (S2) was located along the upland boundary in the upper In addition to the properties of pesticides, the sedimentary process is stream area. Based on the pesticide application date and the local hy- largely dependent on soil erosion particle properties which also control drological conditions, the sediment cores were collected in July 2015 the biological characteristics and the hydrological conditions that affect after the application. Sediment cores of 30-cm were collected from each pesticide transport and degradation (Boyer et al., 2018; Chattopadhyay section using a columnar sampler (PVC tube, 7.5 cm in diameter), and and Chattopadhyay, 2015). Field observations and laboratory experi- samples were sliced into 1-cm intervals to collect a total of 60 samples. ments have shown that the sorption and degradation processes of pes- Samples were transferred to polyethylene bags and were freeze-dried, ticides are directly affected by soil organic matter and the soil aerobic slightly crushed, passed through a 0.147-mm sieve and stored in sealed and anaerobic conditions also have impacts (Aparicio et al., 2018; Dang bags (Ouyang et al., 2017b). et al., 2018). In some high-altitude agricultural watersheds of China, The main types of crops being grown in the watershed are soybean, pesticides and their metabolites are detained in the frozen soil during maize and rice. Prometryn, isoprothiolane, and oxadiazon are the main the winter period, and then they are transported to the river and moved pesticides used in rice paddies, (and oxadiazon is also used), and they downstream during the thawing process that occurs in the spring were used on 7 May, 5 May and 6 July, respectively (Fig. 1b). Atrazine (Ouyang et al., 2017a,b). However, little is known about the long-term was introduced in the 1950s and has been widely used for weed control accumulation and metabolic characteristics of pesticides in sediments in the uplands. Atrazine was used in the uplands on 1 June with a in agricultural watersheds with cold temperature conditions. The dosage of 0.79 kg/ha. The freeze-thaw cycle in the agricultural wa- characteristics of pesticides could have different performance in cold tershed provided the opportunity to preliminarily study the transport of watersheds with a high content of soil organic matter. typical pesticides and to characterize the pesticide metabolites under As a stable medium in the watershed, sediment provides a route cold conditions. As an organic pollutant, the degradation process of map for the historical inversion analysis of a typical pollutant under a atrazine and its impact on environmental health are also main concerns changing environment (Mcmurry et al., 2016). With advances in geo- (Tierney et al., 1999). Based on the land use distribution and transport chemical methods, sediment dating has become a more effective distance, atrazine was selected to accomplish this goal. Atrazine has a method to reconstruct the historical pollution pattern; and the activity half-life of more than 200 days in surface water and a moderately hy- 210 210 226 of Pbex (210Pbex = Pbtot − Ra) is commonly used to calculate drophilic characteristic (its water solubility is 33.8 mg/L at 22 °C, sediment age through a the constant rate of supply model pKa = 1.68, Log Kow = 2.5) (Guo et al., 2016). Atrazine can degrade to (Krishnaswamy et al., 1971; Townsend and Seen, 2012). The results of deisopropyl-atrazine (DIA) and deethyl-atrazine (DEA) (Fig. 1b); both radiometric dating can be integrated with other factors to determine the are especially recalcitrant to biodegradation and have strong leaching temporal patterns of pesticide pollution (Della et al., 2016). Therefore, properties (the water solubility of DIA and DEA is 3200 mg/L and combining the dating results and the concentrations of the pesticides in 670 mg/L, respectively;